In a rack enclosure comprising a backplane across which a plurality of devices, for example, storage disks communicate across a bus, for example, a SCSI bus, one or more power supply units are frequently used to supply power in the form of one or more voltage supply rails to the backplane for use by the devices. With the increasing complexity of configuration of rack enclosures, their continued operation can become more critical and so it becomes important not alone to diagnose faults when they have occurred but also to determine when faults may occur and what their cause might be.
The present invention seeks to mitigate the problems of detecting and diagnosing problems which may occur in a rack enclosure power supply unit.